The reaction between sugars and proteins has been known for some time. As early as the year 1912, Maillard found that glucose and other reducing sugars reacted with amino acids, then stable brown pigments were formed through a series of dehydrations and rearrangements. Further studies have suggested that storing and heat-treating food could also produce such pigments formed from sugars and polypeptides. The formation of such pigments reduces the biological activity of proteins. For related application patents, please see U.S. Ser. No. 08/588,249. The non-enzymatic reaction between reducing sugars and free amino acids can form a stable diketone byproduct, known as the Amadori product. In particular, the amino terminal of the beta-chain of hemoglobin reacts with glucose to form hemoglobin A1c. Like reactions have been found to occur with a variety of other body proteins, such as lens crystallins, collagen and nerve proteins. See, Advanced Glycosylation; Chemistry, Biology and Implications for Diabetes and Aging, Advances in Pharmacology, Vol. 23, pp. 1-34 Academic Press, 1992).
Said reactions are accelerated in the presence of elevated glucose levels, as occur in individuals with diabetes mellitus, but still occur at normal glucose levels. Meanwhile, the aging process is closely related to the formation of lipofuscin. The aging of collagen can be mimicked in vitro by using collagen and glucose. The glucose-induced collagen products capture and react with other proteins, leading to a cross-linking reaction between the proteins. The glucose induced crosslinking reaction produces advanced glycosylation endproducts (AGEs). It is known that AGEs are related to the complications of diabetes, and normal aging process also gives rise to the increase of AGEs. The AGEs inside the body not only have aberrant pathological chemical structure but also can be identified by certain receptors, and thus cause complicated pathological changes related to diabetes and aging.
At present, several successful therapeutic approaches have been achieved based upon intervening in the accumulation of AGEs. One approach is described in U.S. Pat. No. 4,758,583, wherein aminoguanidine and the analogues thereof are used to inhibit the formation of AGEs from its precursors. By reacting with early glycosylation products, the agents prevent the glycosylation products from being further converted into AGEs, and further cross-linking of AGEs with tissues is also inhibited. Efficacy of this approach has been demonstrated in rat animal models of diabetes and aging, including other effects on macrovascular, renal and neural pathology. These data have been reviewed by Vlassara, et al., 1994, Biology of Diseases, “Pathogenic effects of advanced glycosylation: biochemical, biologic and clinical implications for diabetes and aging”, Laboratory Investigation 70:138-151; Brownlee, 1995, “The pathological implications of protein glycation”, Clin. Invest. Med., 18:275-281; and Brownlee, 1995, “Advanced protein glycosylation in diabetes and aging”, Ann. Rev. Med. 46:223-34.
Another approach for controlling AGEs in tissues, especially AGE cross-links (which are responsible for clinical or subclinical pathological changes) that have already been formed and accumulated in tissues, is to reverse or break the formed AGE cross-links. Vassan et al. have proved that this approach involving the breaking of AGEs is effective (vassan, et al., Nature, 1996, Vol. 382(18), 275-278). All of the compounds, formulations and methods disclosed in U.S. Pat. No. 5,656,261 and U.S. application Ser. Nos. 08/588,249 and U.S. Ser. No. 08/848,776 can break the formed AGE cross-links in vivo and in vitro. Studies have demonstrated positive effects of such compounds on cardiovascular diseases resulted from aging (Wolffenbuttel, et al., 1998, “Breakers of Advanced Glycation End Products Restores Large Artery Properties in Experimental Diabetes”, Proc. Nat. Acad. Sci. U.S.A. 95:4630-4634). In these studies, rats diabetic for 9 weeks followed by 1 to 3 weeks administration of an AGE breaker compound resulted in reversal of diabetes-induced increases in large artery stiffness. Parameters that were improved included cardiac output, peripheral resistance, systemic arterial compliance, input impedance of the aorta, and compliance of the carotid artery (U.S. Pat. No. 6,319,934).